Approximately one third of the historical occurrences in CA have been extirpated; threatened by urbanization, road construction, vehicles, grazing, trampling, foot traffic, recreactional activities, erosion, and non-native plants. Several occurrences introduced (22B, 34C, 35B, 36D), but few have survived. See Proceedings of the American Academy of Arts and Sciences 8:368 (1872) for original description.